Precious metal alloy



Patented Sept. 12, 1939 UNITED STATES PATENT OFFICE No Drawing. Application September 15, 1938, Serial No. 230,037

Claims.

This invention relates to precious metal alloys, more particularly to alloys of this type suited for use in dental work and has for its principal object the provision of a'new and improved alloy.

It is a main object of the invention to provide an alloy that can be produced at low cost; is impervious to oral fluids that hasten oxidation and tarnish; that produces no deleterious effect upon oral tissue; and has a light or white color so as not to be unduly noticeable when used in a denture.

Still another object of the invention is to provide an alloy that: melts completely without puddling at temperatures within the range that can be produced by dentists and in dental laboratories so that intricate castings can be successfully formed from it.

Still further object of the invention is to provide a metal that: is hard enough for use in dentures; that can be annealed to facilitate working it, that is capable of taking and retaining a mirror-like polish; and is light in weight so that a denture made from it will not be objectionably heavy.

Further objects of the invention, not specifically mentioned here, will be apparent from the detailed description in which a preferred embodiment of the invention isexplained by way of example and from the claims which follow.

30 I Alloys of the precious metals, particularly gold and silver: and metals of the platinum group are commonly used in dental work in the making of plates, bridge work saddles and backings, inlays and the like. In such alloys gold heretofore has been the principal element. While such alloys are for the most part quite satisfactory for the use intended, they are objectionable as being too expensive particularly since the price of gold has been so-materially increased. Although such gold base alloys are satisfactory in most instances, there are cases where the acidity of the oral fluids quickly attacks the metal to tarnish thesame to an objectionably dark color.

In an effort to reduce the price of alloys used in the making of dentures various combinations have been made employing a substantial percentage of base metal such. as tungsten, chromium, cobalt, etc. and a correspondingly smaller proportion of the precious metals such as gold, silver and platinum. These alloys, while cheaper than a precious metal alloy, have not been altogether satisfactory. Some of the-alloys do not melt completely into liquid state but rather tend to puddle so that the making of a perfect casting 55 of intricate design from the molten metal is difiicult if not impossible. Others of the alloys are too soft and lack the strength required for successful use in dentures. Many of the alloys can be polished only with great difliculty and when polished do not present a mirror-like appearance that is so desirable. I

Most of the alloys of the base metal group will not successfully withstand the action of oral fluids without tarnishing and some of these alloys deleteriously effect the tissues of the oral cavities. Some of these alloys melt only at a temperature higher than the temperatures that can be produced by dentists and dental laboratories with the equipment normally found therein and a special heating equipment is, therefore, required in the use of these alloys. Most of the base metal alloys are rather heavy and as a result, dentures made therefrom in such a manner as to have the requisite strength are objectionably heavy.

The present invention is directed to the provision of a metal alloy which will overcome the objections that can be raised to the alloys available heretofore.

In practicing the teachings of my invention, I follow the practice of the prior art, of which I am aware, of combining palladium and silver. As is well understood, pal1adium is characterized by its tendency to absorb gases, particularly hydrogen, with the result that an alloy containing this element will absorb gases when hot and upon cooling will expel some of the gas, and thereby produce a porous casting unsuited for dentures. This fault in palladium alloys has been recognized heretofore and various efforts have been made to overcome it, but, insofar as I am aware, none of these efforts have been entirely successful.

To the mixture of palladium and silver I add copper, the resulting alloy being harder than either silver or palladium alone and possessing the quality of melting completely without puddling. The copper serves principally as a filler to cheapen the alloy although the copper effects other changes in the characteristics of the alloy. The copper added does not cure the tendency of the palladium silver alloy to absorb gas, though it may reduce it some. i

I have found that by adding a small amount of aluminum to the mixture of palladium silver and copper, the tendency of the alloy to absorb gas can be counteracted and non-porous castings suitable for dentures can thereby be made.

The addition of aluminum to silver hardens the silver materially, and when aluminum is added to a mixture of palladium, silver and copper,

third as much copper as silver can be made.

non-absorbing with a quantity of aluminum sum ciently small that the alloy will not be too hard. One specific alloy comprising 45 parts palladium, 40 parts silver, 13 parts copper and 1 parts of aluminum has been found to be satisfactory for the purpose intended. Such an alloy melts at about 1900 degrees Fahrenheit, a' temperature readily obtainable with equipment usually found in dental laboratories. When melted at this temperature, the alloy passes into a completely liquid state without puddling and intricate castings can be made from it readily by one skilled in the art. Brinell hardness of about 167 and is soft enough to permit it to be worked easily. The hardness of the alloy can be increased by the usual age hardening process. Castings made from the alloy have suflicient resiliency to permit minor adjustments to be made. The alloy is of light weight, having a specific gravity under 12, and dentures made from it are not unduly heavy. The alloy is light in color and may be readily polished to a mirror-like brilliancy that reflects the color of the tissues of the oral cavity. The alloy is non-porous and oral fluids do not attack it to hasten tarnish. The alloy has been found to have no deleterious effect upon the tissues of' the oral cavity. Finally the alloy is relatively inexpensive.

It will be noted that my improved alloy contains no gold. This materially reduces the cost of the alloy which can be produced at from onethird to one-half the cost of known alloys con-' taining a major portion of gold.

While my improved alloy preferably contains substantially equal parts of palladium and silver, other proportions of these elements may be used. The silver content may be increased within the teachings of the invention until there is about twice as much silver as palladium. Preferably The alloy, after annealing has a the copper content is maintained at or near onethird of the silver content although in alloys high in silver less than one-third as much copper as silver is preferable.

The aluminum content of the alloy is not subject to much variation since too much aluminum renders the alloy too hard for dental uses. I have found that in alloys containing less than 50% palladium, the aluminum content can be limited to 1.75 parts out of 100 parts and the alloy will be non-porous and not too hard.

Unlike the base metal alloys of the prior art with which I am familiar, my improved alloy is not dimcult to polish to mirror-like brilliancy.

While I have described my invention by enumerating specific proportions of the metals constituting the alloy, I have done so by way of example and I do not wish to be understood'as limiting myself to the specific proportions named, as these proportions may be changed by one skilled in the art within the teachings of the invention.

Having thus complied with the statutes and described a preferred embodiment of my invention, what I consider new and desire to have protected by Letters Patent is pointed out in the appended claims.

What is claimed is:

1. An alloy composed of from one and onehalf to one and three-quarters parts aluminum, from ten to fifteen parts copper, from thirty to forty-five parts silver and from fifty-eight to thirty-eightparts palladium. l

2. An alloy composed of one and one-half par aluminum, thirteen and one-half parts copper, forty parts silver and forty-five parts palladium.

3. An alloy composed of from one and onehalf to one and three-quarters parts aluminum, from thirteen to fifteen parts copper and the balance silver and palladium in substantially equal amounts. r V

4. An alloy composed of from one and one-half toone and three-quarters parts aluminum, from thirteen to fifteen parts copper, from thirty-nine to forty-five parts silver and the balance palladium.

5. An alloy composed of one and three-quarters parts aluminum, fourteen and one-quarter parts copper, forty-five parts silver and thirtynine parts palladium.

JAMES A. HLGALLON. 

